The present invention relates to a cassette chamber into and from which a cassette stored with objects of treatment, such as semiconductor wafers, is loaded and unloaded.
Generally, in subjecting semiconductor wafers to any of various treatments, such as film formation, etching, thermal oxidation, etc., a cassette stored with a large number of wafers, e.g., 25 wafers, is first loaded into a cassette chamber. Thereafter, each wafer in the cassette is delivered into a process chamber through a transfer chamber by means of a transportation arm in a vacuum.
In setting the cassette in the cassette chamber, the cassette is placed on a stage in the chamber in a manner such that its wafer loading/unloading aperture faces upward. Thereafter, the cassette is rotated substantially through 90.degree. by means of a drawbridge-type drive mechanism in the cassette chamber as it is taken into the chamber, and the wafer loading/unloading aperture having so far been kept upward is oriented in the horizontal direction.
In general, a plurality of cassette chambers, e.g., two chambers, are connected to one transfer chamber that is provided with one transportation arm. Accordingly, each of cassettes in the two cassette chambers is directed so that its horizontally oriented wafer loading/unloading aperture is reoriented in the moving direction of the transportation arm, whereby the single arm can access the individual cassettes in the two chambers.
FIG. 23 shows a cluster tool apparatus, in which semiconductor wafers W are fed into process chambers and treated therein by the aforesaid series of processes of operation. This apparatus mainly comprises two process chambers 2 and 4, one transfer chamber 6 connected to the chambers 2 and 4, and two cassette chambers 8 and 10 connected to the chamber 6. These chambers can communicate with one another by means of gate valves G that can be closed airtightly. As shown in FIG. 24, the transfer chamber 6 contains therein a bendable rotatable transportation arm 12 of, for example, a multi-joint type, which can load and unload semiconductor wafers W stored in cassettes C in the cassette chambers 8 and 10.
In general, each cassette C must be placed on a stage outside a gate door G1 of each corresponding cassette chamber 8 or 10 in a manner such that it faces itself in the X-axis direction of FIG. 23 and that its wafer loading/unloading aperture 14 faces upward (or in the Z-axis direction). In order to take the cassettes C into the cassette chambers 8 and 10 and take out the semiconductor wafers W from the cassettes C in the two cassette chambers 8 and 10 by means of the single transportation arm 12, therefore, each cassette C must be rotated horizontally while being set upright so that the wafer loading/unloading aperture 14 is directed toward the center of the transportation arm 12 (or oriented in a moving direction A).
Apparatuses for this operation are described in, for example, U.S. Pat. Nos. 5,186,594 and 5,507,614. In the apparatus disclosed in U.S. Pat. No. 5,186,594, the cassette C placed on the stage outside the cassette chamber 8, with its wafer loading/unloading aperture 14 upward, is rotated through 90.degree. around the Y-axis of FIG. 23 by means of a drawbridge-type drive mechanism. Thereupon, the cassette C is taken into the chamber 8, and its aperture 14, having so far been kept upward (or in the Z-axis direction), is reoriented in the horizontal direction (X-axis direction). Then, the cassette C is rotated through a predetermined angle .theta. around the Z-axis of FIG. 23 by means of a pivot mechanism, whereupon its wafer loading/unloading aperture 14 is directed toward the center of the arm 12 (see FIG. 25). In the apparatus disclosed in U.S. Pat. No. 5,507,614, on the other hand, a tilted shaft that is oriented at a predetermined angle to the direction of gravity is rotated so that the cassette C can be situated at one operation in a predetermined position with its aperture 14 directed toward the center of the arm 12.
The apparatus stated in U.S. Pat. No. 5,186,594 requires the pivot mechanism as well as the drawbridge-type drive mechanism, that is, it needs use of separate drive mechanisms for rotating the cassette C through 90.degree. around the Y-axis and through the predetermined angle around the Z-axis. Consequently, a lot of complicated drive mechanisms must be used in each cassette chamber, so that the manufacturing cost is high, and more particles are produced. As for the apparatus described in U.S. Pat. No. 5,507,614, it is designed so that the obliquely extending shaft is rotated. As compared with the case in which the cassette is rotated horizontally, therefore, the rotation mechanism section of this apparatus includes more biased portions, so that more particles are produced correspondingly. Since the cassette C is rotated obliquely, moreover, the rotation requires a wide space, so that the chamber is inevitably large-sized.